This invention concerns tubing hangers for horizontal christmas trees and the control of fluid flows from and within such trees.
A tubing hanger is used in oil and gas wells to hang the downhole tubing. In a horizontal christmas tree arrangement it is landed in and makes an annular seal with the christmas tree spool. Control of the production flow is via valves situated on the horizontal christmas tree, separate from the tubing hanger.
There are advantages in relocating the valves associated with the horizontal tree system from the christmas tree assembly itself to the tubing hanger. For example a production master valve located in the tubing hanger remains fully effective, independently of the condition of the tubing hanger/tree seal. Thus it may enable ready replacement of such seals. Moreover, such a valve is retrievable with the tubing hanger, whereas servicing of valves integral to the horizontal tree requires retrieval of the tubing hanger followed by retrieval the tree, a time consuming and costly operation. The positioning of valves in the tubing hanger simplifies the tree design and also enables other valves hitherto normally found in christmas trees to be located remotely from the wellhead, with advantages for installation, servicing and subsequent modification of well components and production flow control/processing equipment.
However relocation of valves from the tree to the tubing hanger is difficult, due to the size of the valves. Gate valves and ball valves are commonly used subsea equipment barriers, and have been used or proposed for use in tubing hangers or similar equipment such as internal tree caps. However the space required to accommodate these valves dictates larger tubing hanger and wellhead designs, with increased capital costs, increased component handling difficulties and hence increased operational costs.
A more effective valve design for use in tubing hangers for horizontal christmas trees is therefore desirable.
According to the invention there is provided a tubing hanger comprising a fluid flow passage and a branch passage having a mouth intersecting with the fluid flow passage, characterized in that a valve seat is disposed in the branch passage proximate to the mouth and a valve closure element is disposed in the fluid flow passage, the closure element being movable across the mouth and co-operating with the valve seat selectively to open or close off fluid communication between the flow passage and branch passage.
This valve configuration is suited to tubing hangers for horizontal christmas tree systems, in which the fluid flow passage comprises a vertically extending through passage connected to the tubing and the branch passage comprises a production fluid side outlet. However, this valve configuration may also be used elsewhere in the tubing hanger, for example in a tubing annulus bypass passage.
In either case, the valve closure element disposed in the fluid flow passage for selective closure of the branch passage in the manner defined above provides a particularly compact valve arrangement. The valve closure element may be movable in use substantially axially of the fluid flow passage, or about an axis extending along the fluid flow passage. Various means can be used to actuate the valve closure element. For example, it may be coupled to an operating shaft extending through a plug in the flow passage. It may comprise gear teeth engageable with a rack on a penetrator extending transversely of the fluid flow passage, or engageable with a pinion gear on a shaft extending lengthwise of the fluid flow passage. Alternatively, the closure element may be hydraulically actuated. The valve closure element may be biased towards the closed position, to provide fail safe closure.
The valve closure element may comprise a sleeve or part sleeve disposed adjacent to a wall of the fluid flow passage. It may contain an aperture selectively alignable with the branch passage mouth to provide said fluid communication. There may be one or more further smaller apertures likewise alignable with the mouth, to provide choked flow between the flow and branch passages.
The valve seat and/or the valve closure element may be mounted for floating movement axially of the branch passage in a manner that provides bi-directional sealing.
Further preferred features and advantages of the invention are in the following description of illustrative embodiments, made with reference to the drawings.